1. Field of the Invention
The present invention is directed generally to a device for clamping a workpiece to a tooling fixture.
2. Description of the Prior Art
The introduction of robotics and computerized numerical control (CNC) machines into the traditional machine shop allows for significant cost reduction in the manufacture of machined items. The time consuming and tedious tasks of controllably moving a cutting tool to shape the three dimensional contours of to-be-produced articles can be transferred from a skilled machinist to a suitably programmed computer. A block of raw stock (usually an elongated block of metal having a rectangular cross section ) is firmly secured into a fixture in the working region of a CNC milling machine. The CNC machine is turned on and a set of pre-programmed machining instructions are supplied to the CNC servomechanism. The machinist is then free to attend to other tasks while the CNC machine proceeds to cut the stock in accordance with the programmed machining instructions. The machinist need not return to the CNC machine until the programmed machining operations are completed. The cost of labor can be reduced by enabling the machinist to attend to more than one such machining operation at a time.
While certain aspects of this type of machining technology have advanced substantially, the step of fixedly securing a workpiece to the workbed of a CNC machine still relies quite often on a conventional vise such as the vise 5 shown in FIG. 1. The vise 5 is formed of a movable jaw 10 having an L-shaped configuration, a fixed jaw 12 of a complementary L-shaped configuration, and an adjusting screw 14 threaded through at least one of the jaws. The adjusting screw 14 can be torqued to create an inwardly directed force F.sub.I between the movable jaw 10 and the fixed jaw 12. The L-shaped jaws may have serrations at their respective ends as shown in FIG. 1. The inwardly directed force F.sub.I may be transmitted through the serrated ends to secure a workpiece 16 as shown.
Since the vise 5 can be used for a multitude of different kinds of workpiece securing operations, its efficiency is rarely questioned in the specific context of CNC machining. One often ignored problem concerns the magnitude of the securing force F.sub.I. The securing force F.sub.I should be sufficiently strong to prevent the workpiece 16 from slipping out of position when a rotating cutting tool 18 belonging to a CNC machine 20 engages against the workpiece. If the machinist fails to tighten the adjusting screw 14 sufficiently, vibrations from the cutting tool 18 may loosen the adjusting screw 14 and thereby allow the workpiece 16 to slip out of position. Subsequent machining operations, that are often performed blindly by the servomechanism of the CNC machine 20, can then fall out of tolerance.
Another problem not normally recognized with respect to the vise 5 in the context of CNC machining, involves the shape and size of the vise 5. The conventional vise 5 is relatively bulky. Provisions are usually made for allowing the movable jaw 10 to travel over considerable distances so that differently sized workpieces can be accomodated. The vise 5 consumes a substantial amount of space because of its bulk and workpiece accomodating features.
In FIG. 1, the cutting tool 18 is shown to be held in a rotating spindle 20a of the CNC machine 20. The spindle 20a is limited in its movement, with respect to the workpiece 16, to operate in the confines of a predetermined working region R.sub.xyz =R.sub.z by R.sub.x by R.sub.y. The region R.sub.xyz is typically defined by the vertical movement limitations of the spindle 20a and the movement limitations of an x-y translation table (not shown) to which the vise 5 is mounted. The workpiece 16 is positioned to protrude beyond the vise jaws, 10 and 12, into the working region R.sub.xyz of the spindle 20a so that desired portions 16a of the workpiece can be accessed and removed by the cutting tool 18. It often occurs that the vise 5, rather than the workpiece 16, consumes a bulk of the limited working region R.sub.xyz. It will be appreciated that this constitutes an inefficient use of the CNC working region R.sub.xyz.
Under current practice, a plurality of machined items 16b are typically produced during one cycling of the CNC machine 20 by forming the original workpiece block 16 as an elongated strip (extending perpendicularly to the plane of FIG. 1). A series of individual items 16b are machined along the elongated strip 16. This strip processing practice helps to reduce manufacturing cost. When the number of individual items 16b that can be produced during a single cycling of the CNC machine 20 is increased the cost per cycle is decreased. Even with such strip processing, the cost per cycle is not fully minimized. The number of items that can be machined in one cycle is limited by the dimensions of the individual items, the dimensions, R.sub.x, R.sub.y and R.sub.z, of the working region R.sub.xyz and also by the space requirements of the vise 5. Because substantial forces often have to be transferred from the screw 14 to the workpiece 16 through the bends of the L-shaped jaws, 10 and 12, the jaws are usually made quite thick. This consumes space that could be otherwise filled with workpieces. Additional space is taken up by the length of the adjusting screw 14 and the travel area provided for the movable jaw 10. More space may be consumed when room has to be provided for accessing a head portion 14a of the adjusting screw 14 in order to tighten and loosen the screw. As such, the total space available in the working region R of the CNC machine is rarely utilized with optimum efficiency. This is particularly the case when each individual item 16b is much smaller than the total space available in the CNC working region R.sub.xyz.